Soluble Mesothelin-Related Peptides
Malignant mesothelioma is a rare cancer of the membranes that cover the outside of internal organs and line body cavities, including the chest (pleural mesothelioma), abdominal cavity (peritoneal mesothelioma), and the heart (pericardial mesothelioma). Between 2,000 and 3,000 new cases are diagnosed annually in the US, and pleural mesothelioma is the most common type, accounting for 90% of all cases. Most cases of pleural mesothelioma—about 70% to 80%—arise in patients with a history of working with asbestos, especially in the shipbuilding, construction, automotive, and fireproofing industries. The disease has a long latency period, meaning that patients usually develop mesothelioma 20 to 50 years after asbestos exposure.
How is the sample collected for testing?A blood sample is taken by needle from a vein in the arm.
Is any test preparation needed to ensure the quality of the sample?No test preparation is needed.
How is it used?This test is limited to patients who have already been diagnosed with malignant mesothelioma. It is not used to diagnose the disease. This test is most often used in conjunction with imaging tests such as positron emission tomography (PET) and computed tomography (CT) to:
- determine if you are responding to treatment,
- see if the disease has spread,
- determine if the disease has returned after you have been treated.
When is it ordered?A physician might order a series of SMRP tests to monitor progression of mesothelioma or its recurrence:
- after you have been diagnosed,
- after you have had surgery to remove tumor tissue in the chest cavity,
- during and/or after chemotherapy or radiation therapy.
What does the test result mean?If a series of SMRP tests show SMRP levels are increasing, it may indicate that mesothelioma has progressed. If the series of tests indicates that SMRP levels are decreasing, you may be responding to therapy. If the levels are unchanged, it may mean that your disease has stabilized.
The interpretation of your SMRP test results will likely be done in conjunction with results from imaging studies. That’s because:
- the test does not always provide physicians with useful information. Patients with other cancers —including lung, ovarian, endometrial, and pancreatic cancers—can have apparent elevated test levels as a result of their cancers producing substances that interfere with the test.
- some patients with epithelial mesothelioma, a form of the disease that affects the cavity lining or membranes, do not produce SMRP.
Is there anything else I should know?This test is not used to diagnose mesothelioma but only used to monitor progression or recurrence. The diagnosis of this disease is often difficult and involves many steps. It usually begins with a review of the patient’s medical history, including a history of exposure to asbestos, and with a complete physical examination. These may be followed by imaging studies of the chest and abdomen, including X-rays and computed tomography (CT) scans, and with lung function tests (LFTs). Diagnosis may be confirmed by examining tissue from a biopsy or fluid from the affected area for malignant cells.
In the US, the Food and Drug Administration has classified the test for SMRP in a special category called a humanitarian device exemption (HDE). The HDE is intended to make medical devices, like laboratory tests, available to patients with rare diseases even though the device has not undergone the usual evaluation for effectiveness. To qualify for a humanitarian device exemption, the device must be intended for use in diseases that occur in fewer than 4000 patients per year. These diseases are so rare that it is not cost effective for a manufacturer to do the extensive evaluation needed for FDA approval. The exemption makes a potentially useful device or test available to the small number of people who might benefit from it.
Nonetheless, manufacturers must show that an exempted device doesn’t pose any threat of illness or injury to you and that its probable benefits outweigh any risks. But since HDE tests have not been validated as effective, they are considered experimental. So before you get the test, your physician must obtain the approval of an institutional review board (IRB), a committee charged with overseeing medical research involving humans and protecting the rights and welfare of study subjects. The manufacturer of the SMRP test has contracted with a national IRB to provide the review and oversight for this test. Your physician will receive certification to use SMRP from that review board.
What is asbestos and how does it cause mesothelioma?Asbestos is a heat- and fire-resistant insulating material that was widely used in construction, shipbuilding, and the automotive industry after 1945 through the 1970s. Workers breathed in the tiny fibers that comprise asbestos. Those fibers entered their pleura, the lining of the chest cavity and lung, and damaged its cells. Mesothelioma develops over a long period of between 15 and 40 years. Research has also shown that family members and others living with workers exposed to asbestos are at an increased risk of developing mesothelioma.